Experience with Hong Kong influenza in tropical areas.
Following the introduction of A2/Hong Kong/68 influenza virus into 2 different susceptible populations residing in Thailand and the Panama Canal Zone, epidemic disease occurred within approximately 1 month. The establishment and transmission of the virus, and the disease it caused, were studied in detail. The rates of progression and extent of overt epidemic disease and the proportions of overt to subclinical infection in the 2 areas were different. In Korat Royal Thai Air Force Base, only 8% of US servicemen became ill, although 13% of them were infected. The epidemic progressed slowly, so that no more than 1.5% of the population were ill at any one time during the 3 months of its recognized presence. In contrast, in the Canal Zone the clinical attack rate approached 50%, and subclinical infection occurred in 5% or less of the population during a 6-week period when absenteeism from schools and work was quite obvious. Factors such as immunization status of the populations and virulence of virus seemed not to be primarily responsible for the differences. Rather, the latter appear to be related to differences in environmental circumstances, with crowding contributing to the higher disease incidence in the Canal Zone.The data show that this variant A2 virus may produce different epidemiological patterns of disease in tropical areas, similar to those observed in temperate zones.
D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks; D005260:Female; D014644:Genetic Variation; D006801:Humans; D007251:Influenza, Human / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D008887:Military Medicine; D010177:Panama Canal Zone; D013785:Thailand; D014329:Tropical Climate; D014774:Virulence